The present invention relates to a vehicle seat comprising a seat portion and a seat pan integrated in the seat portion.
In a frontal vehicle impact, the thorax and the head of a vehicle occupant are moved forward until the forward movement of the occupant is limited by a seat belt. In the subsequent recoil, the thorax and the head bump against the back rest and the head rest of the vehicle seat, respectively. For restraining the vehicle occupant wearing a seat belt, the design of the seat pan integrated in the seat portion of the vehicle seat in addition is of particular importance. The design thereof can support the function of the seat belt to the effect that the so-called xe2x80x9csubmarining effectxe2x80x9d is avoided. In a vehicle impact, the vehicle occupant may plunge into the seat portion of the vehicle seat so deep that the seat belt slips to the area of the abdomen of the occupant, where it can cause severe internal injuries. This effect is conventionally avoided in that the seat pan in the seat foam base of the vehicle seat has a rigid ramp-shaped structure, which influences the rotation of the pelvic bone of the vehicle occupant such that the seat belt is prevented from slipping down to the abdominal area.
The rigid structure of the seat pan can, however, also be noticeable in the normal operation of the vehicle and would thus reduce the comfort properties of the vehicle seat.
From the German Utility Model 296 10 078 a vehicle seat is known, which comprises an actuator with a seat pan pivotally mounted in the seat portion. In the case of a frontal vehicle impact, the angle of inclination of the seat surface adjoining the seat pan is increased due to the swivel movement of the seat pan.
The U.S. Pat. No. 5,695,242 describes a vehicle seat comprising a device by means of which a front part of the seat cushion can be raised in the case of a collision. The device may be an air bag, a mechanical spring-loaded part or a pyrotechnically driven device. The device effects a lifting of the legs of the vehicle occupant and thus reduces the risk of injuries in the area of the lower extremities.
The known systems thus require the presence of numerous mechanical parts and components, whose functional reliability can not always be ensured.
It is an object of the invention to avoid the above-mentioned disadvantages and provide a vehicle seat by means of which the xe2x80x9csubmarining effectxe2x80x9d explained above can be avoided for tall and small occupants in different impact situations.
This object is solved by a vehicle seat comprising a seat portion and a seat pan integrated in the seat portion, which is characterized in that the seat pan is at least partly filled with a viscous mass that can be activated to form a seat ramp.
Suitable viscous masses in particular include those masses which undergo a high change in viscosity by applying an electric or magnetic field. In the following description, these viscous masses will be denoted as electroviscous masses, as well. The change in viscosity advantageously effects a solidification of the viscous mass.
The electroviscous masses suitable in accordance with the invention exhibit an electrorheological or magnetorheological behavior and are known for instance from the field of the steering assistance technologies. Suitable electrologic or magnetorheologic fluids comprise soft polymer particles dispersed in a silicone oil or magnetically soft microspheres of iron, preferably carbony iron, suspended in synthetic hydrocarbon or silicone base fluid.
The electroviscous mass incorporated in the vehicle seat or the seat pan is not noticeable for the vehicle occupant when no voltage is applied. As compared to the seats provided with rigid seat ramps, the vehicle seat thus has clearly improved comfort properties. When the viscous mass incorporated in the seat pan is activated for instance by applying an electric or magnetic field, the stiffening of the viscous mass provides a seat ramp with which the so-called xe2x80x9csubmarining effectxe2x80x9d is avoided.
Due to the very quickly occurring change in state or change in viscosity, the activation of the viscous mass can be effected during the restraining process. The response times of the electroviscous masses preferably lie between 2 and 5 ms. Moreover, the viscous mass can also be activated reversibly by means of an anticipatory sensor system in the vehicle. The time requirements to be satisfied by the activation are distinctly reduced in this embodiment.
The activation of the viscous mass is preferably effected in a predetermined shape, i.e. the viscous mass is incorporated in a cushion which already has the shape of the seat ramp obtained upon activation. In an alternative embodiment, the activation of the viscous mass can also be effected adaptively, i.e. the contour of the mass or the cushion is not changed during the activation of the viscous mass. With this embodiment, particularly high comfort properties can be achieved.
An adaptation of the seat ramp properties to the height of the vehicle occupant can also be achieved by using viscous masses where the change in viscosity is effected in dependence on the loading speed. In smaller persons, the change in viscosity then is less marked than in taller persons, as the latter ones move over the seat at a higher speed. This embodiment is thus based on an activation of the viscous mass by acceleration forces acting on the mass.